1. Field of the Invention
The present invention relates to nonwoven webs. Specifically, the present invention relates to nonwoven webs comprising shaped fibers and a high-absorbency material in fluid communication with said nonwoven web.
2. Description of the Related Art
The use of shaped fibers to form various woven and nonwoven products is known. For example, U.S. Pat. No. 4,129,679 issued Dec. 12, 1978, to Woodings describes regenerated cellulose filaments having a collapsed hollow structure and a multi-limbed cross section. The fibers are said to possess a high capability of water imbibition. The fibers can be formed into woven fabrics like toweling and non-woven fabrics and wadding such as diapers, sanitary napkins, tampons and swabs.
European Patent Application 0 301 874 published Feb. 1, 1989, is directed to cellulosic fibers having a decitex of less than 5.0 and a multi-limbed cross section. The limbs have a length-to-width aspect ratio of at least 2:1. The fibers can be formed into woven, nonwoven, or knitted fabrics and are described as being especially useful for absorbent products.
Similarly, Japanese Kokoku Patent No. SHO 62[1987]-53605 published Nov. 11, 1987, is directed to synthetic fibers having shaped cross sectional views meeting certain criteria. Again, the fibers are said to have excellent water absorptivity when formed into nonwoven products.
When nonwoven webs are employed in disposable absorbent products such as diapers, training pants, adult incontinent products, feminine care products, wound dressings, and the like, the simple ability to absorb a liquid is generally not sufficient to ensure optimum performance in a product. For example, during use, many personal care products are exposed to multiple insults of a liquid. In order to ensure proper absorption of subsequent insults, it is generally desired that the first insult of liquid be not only absorbed but also transported within the absorbent products to areas remote from the point of insult.
Additionally, the ability of a nonwoven web to transport a liquid is desirable for another reason. Specifically, when the nonwoven web is to be employed in an absorbent product, it is often desirable to incorporate into the nonwoven web a high-absorbency material. Such high-absorbency materials are known to those skilled in the art and are generally capable of absorbing many times their weight in a liquid. Thus, much of the total absorbent capacity of an absorbent product, employing such high-absorbency materials, results from the presence of the high-absorbency material. In order for the high-absorbency material to absorb a liquid, the liquid must come into contact with the high-absorbency material. If the nonwoven web incorporating the high-absorbency material is not able to transport a liquid from the point of liquid application, all of the high-absorbency material must be placed in the general area where the liquid to be absorbed will be applied to the nonwoven web. This is not always desirable.
Specifically, when a high concentration of a high-absorbency material is localized in a nonwoven web, it is possible for gel blocking to occur. That is, the high-absorbency material can swell in the localized area to the extent that an essentially liquid-impermeable mass of high-absorbency material is formed. Should this occur, subsequent results cannot be absorbed by the nonwoven web. Accordingly, it is often desirable to more evenly distribute the high-absorbency material in the nonwoven web. For this reason, it is desirable for the nonwoven web to be able to transport a liquid from a point of application to a high-absorbency material located remote from the point of application.
In the past, the ability of a nonwoven web to transport a liquid was generally regulated by adjusting the capillary size of the nonwoven web. Specifically, loosely compacted, relatively low density nonwoven webs were generally not capable of good liquid transport against a pressure, such as a gravitational head, due to the relatively large pore size present within the webs and the correspondingly relatively low capillary pressure. In order to obtain good liquid transport against a pressure, it was generally believed necessary to densify the nonwoven webs to reduce the capillary pore size thereby increasing the capillary pressure and allowing the liquid to be transported farther against a pressure from the point of application. Unfortunately, as a general rule, the higher the density of a nonwoven web, the less able the nonwoven web is to rapidly accept a liquid applied thereto.
When nonwoven webs are employed in absorbent products, it is desirable that the web not only be able to transport a liquid against a pressure but also be able to quickly accept a liquid. Therefore, in order to provide a structure capable of both quickly accepting a liquid and of transporting the liquid against a pressure, it was often thought necessary to provide two layers; one of a relatively loosely compacted, porous nature, able to quickly accept a liquid, and one of a higher density, compacted nature, capable of transporting the liquid against a pressure.